Microtubules:  During early stage I, oocyte MTs become more evenly dispersed throughout the cytoplasm (JPEG: 68 kB). MTs are often observed in  association with perinuclear mitochondrial aggregates that precede formation of the mitochondrial mass (JPEG: 75 kB). Acetylated MTs are also dispersed throughout the cytoplasm, but are often concentrated in both the perinuclear and cortical cytoplasm  (JPEG: 56 kB). Staining with antibodies to g-tubulin reveal that this centrosomal protein is dispersed between 2-12 cytoplasmic foci (JPEG: 47 kB), which do not function as MTOCs during recovery from cold-induced MT disassembly (JPEG: 42 kB), suggesting that the maternal centrosome is inactivated during early stage I of oogenesis.

By mid-late stage I, oocytes contain a dense array of cytoplasmic MTs (JPEG: 83 kB; AVI or QT: 1.7 MB). Estimates of the tubulin pool and polymer content suggest that a single stage I oocyte contains up to 60 cm of MT polymer! Little order is apparent in this MT array, and there is no evidence of a functional centrosome or MTOC in oocytes of this stage. The complexity of this MT array is best appreciated by viewing 3-D reconstructions of MT organization in a mid-stage I oocyte (JPEG; AVI; or QT: 2.0 MB). MTs are associated with the mitochondrial mass, surrounding and penetrating this unique aggregate of organelles and linking it to perinuclear and cortical MTs. Acetylated MTs form complex networks surrounding the GV and in the cortical cytoplasm, and bundles of acetylated MTs extend between the GV and cortex (JPEG: 53 kB; in serial Z-section: AVI or QT: 1.5 MB) (in 3-D reconstructions: JPEG;  AVI, or QT: 2.0 MB).  Acetylated MTs are also associated with the mitochondrial mass and link this aggregate of organelles to the GV and cortex (JPEG: 57 kB).

F-actin: The cortex of early stage I oocytes stains brightly with fluorescent phalloidin, indicating a concentration of f-actin in the cortical cytoplasm. In addition, a network of cytoplasmic actin cables first appears during early stage I (JPEG: 55 kB).These cables are sparsely scattered in the cytoplasm, and do not appear to be associated with discrete organizing centers. The complexity and density of this network increases during oocyte growth and differentiation. Assembly of the cytoplasmic network of actin cables is accompanied by the appearance of F-actin in the oocyte nucleus, or GV. Initially, F-actin appears in patches surrounding nuclear inclusions, such as nucleoli.

By mid-late stage I, the cortex and GV both stain brightly with fluorescent phalloidin (JPEG: 52 kB), and a dense network of actin cables extends throughout the cytoplasm (JPEG: 68 kB; stereo JPEG; AVI or QT: 1.5 MB). Actin cables are associated with the mitochondrial mass, which also exhibits a diffuse staining (JPEG: 69 kB).